Plastic lenses are now becoming a mainstream in the field of spectacle lenses owing to their such features as light in weight, safety, easy workability and fashionable facets that are not obtained with the glass lenses.
The plastic lenses, however, have a defect in that they are vulnerable to be scarred. It is, therefore, a generally accepted practice to coat the surfaces of the plastic resins with a silicone film. The silicone coating (called hard coating) is, usually, formed by applying a coating agent comprising, chiefly, fine inorganic oxide particles, a polymerizable organosilane compound, a polymerizing catalyst, an acid aqueous solution and an organic solvent onto the surfaces of the plastic lenses, followed by heating to cure the coating agent as well as to volatilize the organic solvent (JP-B-57-2735). Attempts have been made to improve the coating agents of this kind, such as improving the refractive index and preservation stability (pamphlet of International Laid-Open 01/42381).